The subject matter disclosed herein relates to rotary-winged aircraft. More specifically, the subject matter disclosed herein relates to actuation of control surfaces of rotary-winged aircraft rotor blades.
Rotary-winged aircraft, such as helicopters, often utilize movable surfaces such as flaps on the blades of the main rotor of the helicopter. Movement of these flaps, such as rotation of the flaps about an axis, improves performance of the rotor in certain flight conditions. Typically, the flaps are moved via linear actuators either directly connected to the flap (chordwise) or operating through a bell crank mechanism (spanwise). The linear actuators are most often constructed using ball screws or roller screws driven by brushless DC motors. To convert the linear motion of the actuator into the desired rotary motion of the flap, it is necessary to connect the actuator to the flap via mechanical linkages and/or bell cranks. These additional components are costly and increase system weight. Further, due to the rotating nature of the rotor blade, the linkages and bell cranks are subject to high centrifugal forces. To offset these forces, the addition of balance masses is necessary to equalize the centrifugal forces during operation, further adding weight to the system.
Further, the linear actuator components such as motor bearings, rollerscrew, and sliding parts such as the output shaft are lubricated by oil or grease contained in the actuator. Such lubricants are affected by high centrifugal forces and tend to migrate to a radially outboard end of the actuator, leaving portions of the actuator without adequate lubrication. Grease and oil are also affected by operating temperature, with low temperatures causing the grease to thicken, resulting in sluggish operation. Also, in a linear actuator the internal volume of the actuator changes during operation, so a complete oil fill of the actuator is not a practical solution, and the oil fill may be subject to leakage during operation.